1984 75 hp Mercury - Great Find but is it Enough Power for a 18 foot Maxum Bowrider?

[@dsciarrino3663]

Sweet Eng

[@stanleyfoxx3227]

Very nice looking engine though. Nice find for sure! I have had the pleasure of working on exact motor 2yrs ago. A friend of mine bought a 1985 75hp Mercury, 4 cyl, same cowling style everything, for a 15 ft glasstream bass boat rated for 75hp. It was a pretty good fit. I thought just a little heavy as it sure set the rear of boat down in water compared to exact boat with 50hp 2cyl Johnson motor without trim. His 75 Mercury did have trim which added to the weight. We had put a trigger assembly and switch box and carb clean to get to smooth perfect running on the motor. It is a smooth engine with unique inline 4 sound versus other Johnson motors I been around (2cyl and V4’s). Good luck with it. Keep us posted Sir! Btw. Nice job getting all the controls and panel. That may come in handy one day as parts. Save everything. PS. Astounding at the difference in that 75 hp and the older 1960’s vintage 75 hp V4 Johnson you did some videos on. Haha. Those vintage motors are mammoth in size and weight at similar hp.

[@LivetofishOutboardRepair]

Stanley… Yea for sure I felt very lucky to find this one. It’s very clean for its age. Im sure I will find another boat or a buyer for this motor if it’s not a good match for the Maxum.

[@goldenguy62]

Good engines, but you will need more for that bow rider. I don’t even think that 75 will get it up on plane. In my opinion, you need at least a 150 for that boat.

[@LivetofishOutboardRepair]

According to the coast guard safety rating only allowed up to 90 hp for this boat. I hope 75 hp will be Ok.

[@giloquendo]

Great video quick question on the mercury I have the same motor but the serial number are damaged what's the serial number on your motor just to get some parts

[@LivetofishOutboardRepair]

Gilfredo Oquendo… The Serial Number is 6502920. I hope this helps. Good Luck and thanks for watching.

[@AM-cl7cz]

Great videos. Just wondering if I can ask you some advice about my motor which is the same one. Having troubles with it hitting wot. If you have time that would be great 👍

[@LivetofishOutboardRepair]

A M …. I would start with a compresssion test before diagnosing your ignition system. Then Check the resistance and peak voltage outputs on the Stator, trigger and switchbox. If everything checks out then start looking at fuel related issues, fuel pump, old fuel, carb jets etc. Make sure you have good compression first before anything else. If you have low compression on any cylinder or have a variance of more than 10% between cylinders you won’t need to look much further. My email address is [e-mail] if you want to contact me. Here is a video on diagnosing your ignition system. kzbin.info/www/bejne/f6mycpqDitOlfKs

[@AM-cl7cz]

@livetofish Outboard Repair many thanks for the quick response 👍. I'll do a video of my checks for you. I've just replaced the trigger, stator, and switch box. Compression was great but I'll send a video with all the checks ✔️ ✅️

[@LivetofishOutboardRepair]

@@AM-cl7cz sounds good. Good luck. I hope you find a solution.

[@AM-cl7cz]

@@LivetofishOutboardRepair I've uploaded a video under my profile youtube

[@LivetofishOutboardRepair]

A M …. Did you happen to verify your Peak Voltage outputs? You may need a DVA adaptor if your volt meter can’t read peak voltage. If all components have good voltage outputs then I would start diagnosing your fuel system, including your fuel pump. You stated the carbs have been rebuilt but may still have a blockage in a high speed jet. Do the rpm’s pick up at full throttle when you squeeze the primer bulb? If so, it’s most likely a problem with the fuel pump.

[@haydencarter4786]

Hi could you tell us or show how to remove the release valve for the hydrolic trim please I’m trying to remove the unit on my 75 and having trouble removing the trim pressure release valve.

[@LivetofishOutboardRepair]

Hayden Carter… I don’t believe you can completely remove the stock relief valve because the hex head is to large to go through the hole on the bracket. I was able to get mine out by grinding the hex head into a circle and then melting a slot with a hot screwdriver into the head of the plastic valve.

[@haydencarter4786]

@@LivetofishOutboardRepair ok thank you for reply. Could we have your email so can send photos to you and communicate more that would be great 👍

[@LivetofishOutboardRepair]

Heyden Carter …. My email address is [e-mail]

[@mikerea678]

Does that motor have a regulator? I have changed the rectifier as my identical motor is producing too high a voltage, but I can’t seem to find where the regulator is located?

[@LivetofishOutboardRepair]

Michael Rea… This motor does not have a voltage regulator. It only has a Stator, trigger, rectifier and switchbox.

[@mikerea678]

@@LivetofishOutboardRepair thank you! Do you know where I can find the ground wires on this motor?

[@LivetofishOutboardRepair]

Michael Rea … I’m not sure but I think there should be a main ground wire under the main bracket covering the coils. It’s under one or both of the bolts at the bottom of lower cowling.

[@brianfoster9329]

My exact motor runs at 17 volts and did some digging after replacing rectifier and had some mixed answers saying could be your battery and some saying rectifier or the stator and some even say it was normal. But couldn't imagine it's normal. With my fish finder being on the same battery it was making the finder do some strange things.

[@stanleyfoxx3227]

I am going to say it would be a little bit small on engine size for any amount of speed or quick acceleration. Depending on your desired use for the boat, speed, distance, ect a bigger motor might be better. You need to try look up the rated hp for your boat. My guess would be between 130 and 150 hp depending on beam width. Stay with in 75 percent of max hp for any good performance. A underpowered boat over works the motor.

[@LivetofishOutboardRepair]

Stanley… I think the max hp rating for this Maxum is 150 hp but I need to verify. I haven’t looked at the Coastguard tag for max weight and hp yet. The boat is covered and It’s like 15 degrees outside so I’m not motivated to uncover it to look. This 18 ft boat originally had a 90 hp Force and depending on the weight and beam 90 may be the max hp but the tag will tell me for sure. I’ve seen information that the weight of the boat could be anywhere from 1500 lbs - 1820 lbs. if it’s closer to 1520 lbs then the 75 Hp Merc might be ok if you use the 20 - 40 lb/ hp rule of thumb. 1520 / 20 = 76 hp. On the other hand if the boat weights 1820 lbs then 1820 / 20 = 91 hp. So I really need to find out what the rating for max really is on this particular boat or the actual weight of the boat. Thanks for watching and commenting. I appreciate your experience and believe you are correct. If the 75 is to small I can always flip the motor and find a larger one.

[@stanleyfoxx3227]

@@LivetofishOutboardRepair 15 degrees! Shew I wouldn’t be going out there either. It is mid 30’s here in Tennessee and it requires alot of motivation to get ready for outdoor projects. Even if the boat is rated like we are thinking it might be worth the effort to mount up the Mercury 75 just to test the motor well and it would give you a chance to see how you like the boat in water and what it’s behavior is along with seeing if it has any leaks ect around the bulkheads and thru hull fittings. If the 90hp force was a Mercury mfg’d motor the throttle/shift cables and wiring might be similar enough to easily hook up with little effort. Good luck however you decide to proceed! Either way since you got a good deal on motor you can’t go wrong. I bet the gentleman with motor wanted a jet drive motor to go shallow since you mentioned duck boat was his desire. If so I bet that motor is fully operational with no hidden faults and the reason to sale motor was it wasn’t the style he wanted. It does look very nice 👍.

[@LivetofishOutboardRepair]

@@stanleyfoxx3227 Your spot on and read my mind. I’m going to look for a jack plate for the boat so I can easily test this motor and maybe even that Old Fat 50 Johnson. I just can’t wait for the ice to thaw and spring to arrive.

[@bassneckfishing2505]

What's the length of the boat

[@LivetofishOutboardRepair]

Bassneck… it’s 18’ long.

[@bassneckfishing2505]

Yeah it will be under power

[@LivetofishOutboardRepair]

Bassneck … Thanks for letting me know. At least it will make a good motor for someone.

[@bassneckfishing2505]

Yes it will I have a 1993 75hp mercury on my bass boat 15.5 foot

[@stanleyfoxx3227]

I am going to say it would be a little bit small on engine size for any amount of speed or quick acceleration. Depending on your desired use for the boat, speed, distance, ect a bigger motor might be better. You need to try look up the rated hp for your boat. My guess would be between 130 and 150 hp depending on beam width. Stay with in 75 percent of max hp for any good performance. A underpowered boat over works the motor.

[@danielrobert7181]

The original offering was a happy compromise. Your 75 hp is definitely on the weak side.

[@LivetofishOutboardRepair]

Daniel Robert…. Thanks for chiming in. I appreciate your opinion and tend to agree. It may be a bit disappointing but I’m hoping it will get up on plane with two people and maybe go 25 mph. What do you think?

[@danielrobert7181]

@@LivetofishOutboardRepair You may somewhat offset that power deficit by playing around with different pitch, diameter and rake props but there is no free lunch here: improving your hole shot performance will reduce your top speed and vice-versa. Anyway in this trial and error process, do not allow your motor to rev much above 6000 rpms (you need a tachometer) and be realistic on what performance improvement prop swapping can achieve. A word of caution: in order to promote quick planing some advocate adding hydrofoils to the motor lower unit. My experience is that such a device usually outbalances the hull which then starts porpoising and gets rather unstable. If you want to go that route, you would be better off adding extended flaps on each side at the base of the transom. Finally, let's say that some advertised outboard HP ratings are deceiving, Most players in the industry switched around 1986 from rating their motors power's at the flywheel to rating it at the propeller: the former method giving consistently higher numbers over the latter since that last one had to deal with power loss due to gear system induced friction. Consequently in comparison your '84 Mercury would probably have been rated at 70 HP in 1991. Sorry but that just increases the HP gap between your motor and what Maxum promoted for that hull.Mind you, if you just want to cruise around (no water skiing) your motor may very well do the trick if you pay attention to reducing to a minimum the weigh on board and insuring its proper distribution in the boat. Happy boating !

[@LivetofishOutboardRepair]

@@danielrobert7181 Your response was very educational and eye opening. Thank you for watching and commenting. I will take all your great points into consideration. Maybe even wait for another larger hp motor to come along. I just really liked this 75 hp. It is in very nice shape for its age but maybe just not the right motor for this boat. Thanks again!